1. Field of the Invention
The present invention relates to an optical element, and more particularly to an optical element used in image pickup apparatus such as video cameras or electronic cameras for obtaining image information by discretely sampling spatial image information by a solid state image sensing device or an image pickup tube, etc.
2. Related Background Art
A variety of image pickup systems have been developed heretofore for obtaining image information by optically spatially sampling an image of an object, for example, by a solid state image sensing device or an image pickup tube in video cameras, electronic cameras, etc.
Since the solid state image sensing devices, image pickup tubes, etc. of this kind demonstrate high spectral sensitivity in the long wavelength region, there is a need to shut off infrared rays etc. in the long wavelength region. For that purpose, the conventional image pickup systems employed a taking optical system including a filter for cutting light in the infrared region.
If an object should include a component of a higher frequency than the half of the sampling frequency for obtaining image information using the solid state image sensing device or the like, an image would have a structure or a pseudo color which the object did not originally have, thereby degrading the quality of image. Therefore, the conventional image pickup systems were arranged to include an optical low-pass filter for shutting off high frequency components.
However, when the image pickup systems had separate members of the infrared cut filter, the optical low-pass filter, and the lens, there were problems of increasing the size and weight of total image pickup system and also increasing the cost.